The onboard electrical system of a modern vehicle having a plurality of electrical consumers is extraordinarily complex. Great care is already required during the design of such an onboard electrical system in order to guarantee high operational reliability over the lifetime of the vehicle. In spite of the care taken during the design of the onboard electrical system, faults may not be prevented from occurring in the onboard electrical system during the lifetime of the vehicle. Fault sources are, for example, impermissible strain on components of the onboard electrical system and/or inadequate maintenance of the vehicle. A typical fault is a shunt, which results in uncontrolled current flow. In the event of adverse circumstances, this may result in a smoldering fire and even destruction of the vehicle.
The onboard electrical system of a modern vehicle includes at least one control unit, which may also recognize such faults in a vehicle which is put into operation. However, a problem may occur during a long operating pause of the vehicle if the control unit which performs the fault test is turned off. In spite of shutdown of the vehicle, at least parts of the onboard electrical system are still connected to the battery. A shunt of the parts of the onboard electrical system which are still under voltage and thermal corrosion caused by the shunt are no longer able to be readily recognized, however.